Stirling is also a well-reviewed author of her memoir The Only Pirate at the Party. She has been very open about her struggles with anorexia and depression, as well as the pain she felt when her father died in January after battling cancer.
PEOPLE’s special issue 25 Seasons of Dancing with The Stars is out Sept. 15
Stirling had always considered her sister to be her best friend. But one day, when she was 23, YouTube’s dancing violinist realized the two college roommates had become “complete strangers.”
“I saw my relationships deteriorating with my sister Brooke,” Stirling told PEOPLE. “I’d become miserable and self-absorbed about my body. That’s when it hit me that I had a problem.”
It was then that Stirling first admitted to herself that she was anorexic and – due to the lack of nutrients – depressed.
“Once I admitted that to myself, I was able to start the process of change,” said Stirling, who relied on group therapy and her Mormon faith as she found her way back to a healthy body weight.
“I believe anyone can find happiness. It just takes a lot of work,” she said.
And now the violinist – who is one of the highest paid content creators on YouTube —is not only close with her sister again, but they also worked together on Stirling’s memoir.
“Getting to write this book with my sister was amazing. She’s an incredible writer and getting to do this with her … we were so sad when it was over,” Stirling said of collaborating on the New York Times bestseller. “My favorite thing about the success I’ve found is that I get to share it with my family and the ones that I love.”
The Season 25 finale of Dancing with the Stars airs Tuesday at 9 p.m. ET on ABC.